Silver halide emulsions with increased sensitivity



United States PatentOfiiice 3,3l8,702. Patented May 9, 1967 4 Claims.(61. 96-107 The invention relates to a method of increasing thesensitivity of photographic silver halide emulsions.

Numerous compounds are known which can be used as additives to theemulsion or developer to increase the sensitivity of a photographiclayer. Many different terms are used for substances that have thiseifect, e.g., chemical sensitizers or activators. The best known classof substances in this field are polyalkylene oxides, in particularpolyethylene oxides and water-soluble onium compounds such .asquaternary .ammonium-, phosphoniumand sulphonium salts or combinationsthereof or derivatives of thiourea, for example, thiouronium salts.

.The maximum sensitivities obtained in silver halide emulsions by theaddition of the above mentioned compounds presupposes that the silverhalide emulsions have been activated by treatment with noble metalsalts, especially gold salts.

The most commonly used combination for gold sensitization consists ofgold-(IID-salts and thiocyanate or thiosulphate, although the solutionsof thiocyanate are not very stable and those of thiosulphate aredifficult to prepare. Reaction kinetic investigations, e.g., byP-rotass,

Bjirrum and Kirschner (Z. Wiss. Angew. Phot. Kine l, n

455 (1956)) on gold complexes with thiocyanate ions admit of theassumption that sensitization is caused by a controlled, slowdecomposition of the Au-(D-complexes in which the thiocyanate ionsparticipate. The mechanism of this sensitization process is not certainsince many reaction components are involved, such as metallic gold,Au-(I)-, Au-'(IlI)- and thiocyanate ions, dithiocyanogen and additionalsulphur degradation products including thiosulphate and gelatine.

Moreover, a considerable excess of thiocyanate ions is required tostabilize the gold(I) complex and obtain maximum sensitivity of thesilver halide emulsions. This method thus has numerous disadvantages. Aconsiderable amount of the gold-(Ill) salts are bound by the gelatin,partly by absorption and partly by complex formation; another amount isreduced to metallic gold and lost for chemical sensitization. Inaddition the large excess of thiocyanate impairs the stability of thelatent image after exposure. a

It has now been found that a combined noble metal sensitization andreduction ripening of silver halide emulsions is obtained, whileavoiding the aforesaid disadvant ages, if the after-ripening isperformed with salts of noble metals of the VIII group of the periodicsystems of the elements having an atomic weight greater than 100 or withsalts of gold, in the presence of nit-rilotriacetic acid or its salts.

The nature of the cation of the nitrilotriacetic acid is not criticaland can be varied as desired, suitable cations are, for example, thoseof sodium, potassium, ammonium and the like.

Suitable noble metal salts of the group V111 of the periodic system areplatinum, palladium and iridium salts, or mixtures of these salts.

The invention can be used on any photographic silver halide emulsion.The silver halide can consist of silver chloride, silver bromide, silveriodide or of mixtures thereof; however, silver bromoiodide emulsions arepre ferred. These emulsions can be chemically sensitized additionally,for example, with sulfur compounds, with polyalkylene oxides, withwater-soluble onium compounds or with combinations of polyethyleneoxides and onium compounds. In addition, they can be opticallysensitized, e.g., by means of methinecyanine, merocyanine, rhodacyaninedyes and the like.

As stabilizer, it is possible to apply organic mercapto compounds,quaternary benzthiazoles, triazoles, tetraazaindolizines and the like.

An additional advantage of the process according to the invention isthat the sensitized emulsion can be used for the production ofbl-ack-and-white or color photo,- graphic materials, it being possiblein the latter case to incorporate hydrophobic or hydrophilic colorcouplers into the emulsion layer.

The noble metal salts and the nitrilotriacetic acid salts can be addedto the emulsions at any stage of the preparation of the emulsion butbefore or during the afterripening. The nitrilotriacetic acid can beadded in dissolved or in solid form before, during or after adding thenoble metal salt. tions of the noble metal salt, for example,gold-III-chloride and of nitrilotriacetic acid. The nitrilotriaceticacid compounds or its salts are used in concentrations of 0.1 g. to 5 g.per 1 kg. of emulsion, advantageously about 0.1-0.5 g./kg. The optimumquantity to be added depends on the nature of the emulsion. It can bedeter mined without any diificulty by means of a few tests.

The manner in which the process according to the invention is used isshown by the following examples:

EXAMPLE 1 A silver chloride-bromoiodide-gelatin emulsion with molpercent of silver bromide and 8 mol percent of silver iodide, whichcontains 50 g. of silver per liter and which further contains potassiumbromide and sulfur compounds for chemical ripening is divided, beforethe after-ripening, into 2 samples:

Sample A serves as comparison sample. Before after ripening, to sample Bis added per liter of emulsion a mixture of 5 ml. of a 10% solution ofsodium nitrilotriacetate and 0.08% gold-III-chloride.

After the two samples have been after-ripened at a pH=5.86.0 maximumsensitivity is reached, a wetting agent and a stabiliser, e.g., of thetetraazaindolizine type, are added and the emulsion applied onto a papersupport.

The two samples are exposed to light and they are developed of thefollowing composition:

It is also possible to add a mixture of solu-,

G. p-Methylaminophenol l Hydroquinone 3 Anhydrous sodium sulphate 13Anhydrous sodium carbonate 26 Potassium bromide 1 Water to make 1000 ml.

The result is shown in Table I:

TABLE I Increase in Fogging Gamma sensitivity Sample A 0 DIN 0. 02 2. 0Sample B +4 DIN 0. 04 1.8

As regards the sensitivity data, it is to be pointed out that anincrease in the sensitivity of 3 lDIN corresponds to an increase by oneaperture.

EXAMPLE 2 A highly sensitive ammonia silver bromide emulsion with 2 molpercent of silver iodide, containing silver halides equivalent to 60 g.of silver per liter, is prepared as in Example 1 and beforeafter-ripening divided into two samples A and B.

Sample A serves as comparison sample. The following mixture is added tosample B per liter before the after-ripening: 5 ml. of a solution ofsodium nitrilotriacetate and 1.3 ml. of a 0.08% gold-III-chloridesolution.

The samples are after-ripened to maximum sensitivity, at a temperatureof about 50 C. and a pH of 6.8. Thereafter a wetting agent and astabiliser, e.g., of the tetraazaindolinzine type, are added and thesamples are cast onto a support of cellulose aceto butyrate.

The samples are exposed to light and they are developed for 5 minutes atC. in an X-ray developer. The result is shown in Table II:

A highly sensitive negative silver bromoiodide gelatin emulsion with 4mol percent of silver iodide, which contains silver halides equivalentto 55 g. of silver per liter and which further contains bromide, sulfurcompounds and the like as chemical sensitizers is divided beforeafter-ripening into three samples A, B and C.

Sample A is the comparison sample. To sample B is added the followingmixture per liter: 3 ml. of a 10% solution of sodium nitrilotriacetateand 0.5 ml. of a 0.08% gold-III-chloride solution.

Sample C is prepared as sample B, but only 1 ml. of the 0.08%gold-HI-chloride solution is added.

The samples are after-ripened at a pH of 6.8 and cast onto a filmsupport, as described in Example 2.

The three samples are then exposed to light and they are developed in anusual p-methylaminophenol hydroquinone developer for 10 minutes at 20 C.

The result is shown in Table III.

A silver bromoiodide gelatin emulsion of medium sensitivity with 6 molpercent of silver iodide containing silver halide equivalent to 45 g. ofsilver per liter is divided before the after-ripening into two samples Aand B.

Sample A is the comparison sample. To sample B is added the followingmixture per liter of emulsion: 3.5 ml. of a 10% solution of sodiumnitrilotriacetate and 1 ml. of a 0.08% gold-III-chloride solution.

The samples are after-ripened at about 55 C. and at a pH of 6.8 and theyare cast onto a sheet-like support of polyethyleneterephthalate.

The two samples are exposed to light and developed for 10 minutes at 20C. in a usual p-methylaminopheuolhydroquinone developer. The result isshown in Table IV.

TABLE IV Increase in Fogging Gamma sensitivity Sample A 0 0.06 005Sample B +2 DIN 0. 06 0. [:5

It will be clear to those skilled in this art that the practice of theinvention lends itself readily to a number of useful modifications inmethod, material, etc. For example, the noble metal salts are notlimited to the previously mentioned, because it is possible to use anysuitable salt which is soluble in water or lower alcohols. Suchcompounds are: gold halides, such as auric chloride, or complex goldhalides, such as potassium chloroaurate (KAuOl and sodium chloroaurate(NaAuCl However, gold compounds, such as auric sulfate, are practicallyas useful as the gold halides. Aurous, as well as auric compounds can beused. Complex gold salts, such as alkali metal aurous thiosulfates,alkali metal aurous sulfites (e.g., sodium or potassium aurousthiosulfate and sodium or potassium aurous thiosulfate and sodium orpotassium aurous sulfite). Potassium chloroaurite, potassiumbromoaurite, potassium iodoaurite, or the corresponding sodium, calcium,strontium, cadmium or gallium salts can also be used.Pyridinotrichloro-gold, ethylenediaminebis-trichloro gold,diethyl-monobromo-gold and diethyl gold acetone and gold complexes withsulfur compounds such as are commonly present in gelatin, e.g., the goldthiosinamine complexes, can also be used. Suitable salts of noble metalsof the VIII group are ammonium or potassium, chloropalladate, ammonium,sodium and potassium chloropl-atinate, ammonium potassium and sodiumbromoplatinate, ammonium chlororhodate, ammonium chlororuthenate,ammonium chloroiridate, ammonium, potassium and sodium chloroplatinite,ammonium, potassium and sodium chloropalladite, etc.

The after-ripening of the emulsion with the noble metal salt and theo-hydroxybenxylamine compounds is performed at an appropriatetemperature particularly between 30 and 65 C. During after-ripening thepH of the emulsion is advantageously adjusted to the acid side ofneutrality preferably between S and 7. Maintenance of the emulsion onthe acid side of neutriality during coating of the emulsion is alsopreferred.

The noble metal salts are employed in an amount below that whichproduces a substantial fog. In practicing the present invention, aquantity of the noble metal salt is employed, equivalent to between 0.1and 50 mg. of the noble metal per mol of silver halide in the emulsion.The noble metal compounds are preferably incorporated in the emulsionsin the form of their solutions in a suitable solvent such as water,methyl alcohol, ethyl alcohol or the like.

We claim:

1. A process for increasing the sensitivity of silver halide emulsions,characterized by performing the chemical ripening with a mixture ofnoble metal salts and nitrilotriacetic acid or a mixture or noble metalsalts and salts of nitrilotriacetic acid.

2. A process according to claim 1, wherein the noble metal is gold.

3. A process according to claim 2, wherein the emulsions containadditionally as chemical sensitizers sulphur compounds, onium compoundsor polyalkylene oxides.

4. A process according to claim 1, wherein tetraazaindolizinestabilizers are added to the emulsions.

No references cited.

NORMAN G. TORCHIN, Primary Examiner.

J. RAUBITSCHEK, Assistant Examiner.

1. A PROCESS FOR INCREASING THE SENSITIVITY OF SILVER HALIDE EMULSIONS,CHARACTERIZED BY PERFORMING THE CHEMICAL RIPENING WITH A MIXTURE OFNOBLE METAL SALTS AND NITRILOTRIACETIC ACID OR A MIXTURE OR NOBLE METALSALTS AND SALTS OF NITRILOTRIACETIC ACID.